1. Field of the Invention
This invention relates to a constant pressure printing mechanism for a portable label printing machine, or the like (hereinafter a labeler). The mechanism regulates printing pressure for obtaining clear and precise printing of labels without differences in the darkness of the printed characters on labels and without double printing.
2. Description of the Prior Art
In conventional labelers, a hand operated lever and a printing lever for carrying a printing head integrally form a working lever. A printing head is attached to the front end of the printing lever. The working lever is pivotally secured to the machine frame. The printing lever carrying the printing head is moved, and more particularly, turned downward, when the hand lever is squeezed. This moves the type faces at the underside of the printing head into contact with the surface of a tape-like label strip that is carried on a platen, thereby printing the labels.
In conventional labelers, however, the intensity of the squeeze of the hand lever directly influences the pressure of the printing stroke. The darkness of the printed characters is liable to vary according to the intensity of the squeezing force applied to the hand lever. Further, when the hand lever is squeezed too strongly and/or quickly, the platen is struck with great force and the printing head bounces on the label placed on the platen causing double printing. Precise printing is thus difficult to achieve.
In the past, even when labels were somewhat indistinctly printed by conventional labelers, they were accepted because customers can read them when they purchase commodities and cashiers can also read them when they total the purchases. In recent years, the figures, symbols (bar codes, OCR characters, etc.), and the like, that are being printed on labels are being read by computerized optical readers in place of cashiers in order to put what is called POS (point of sales) system into practice. In this system, information concerning stocks, sales, customers' data, profit and loss, and other management data are memorized and processed by electronic computers. To enable accurate machine reading of labels, it has become necessary for the labels to always be printed with clear consistent quality, precise characters and symbols.